This invention relates to a one-piece powerboat hull construction which has greatly enhanced performance characteristics.
Over the years the design of watercraft has evolved dramatically. Many design changes have been enabled by the advent of new construction materials or manufacturing techniques that have transformed the cumbersome wooden powerboats of old into the sleek and hydrodynamic powerboats of today. Powerboats today have hulls that are typically of one-piece molded construction and which have sleek dynamic style lines.
One of the most popular hull designs in use today is the V-bottom hull. The V-bottom hull is generally preferred by pleasure boaters for its smooth ride in rougher, choppy water and also for its excellent handling characteristics particularly when executing turns.
The same V-bottom construction which provides generally preferred performance characteristics, however, also possesses drawbacks in comparison to a fully or generally planar bottom. Specifically, the V-shape of the hull which provides excellent hydrodynamic performance as it slices through the water also requires the addition of modified outside surfaces to provide adequate lift when the boat is operated at higher running speeds. For this reason, the bottom surface of the V-type hull also typically includes a plurality of longitudinally extending lifting strakes which include one surface disposed generally parallel to the surface of the water and a second surface disposed at about right angles to the first surface. This is to be distinguished from the generally almost oblique orientation of an unmodified V-bottom hull when viewed in cross-section.
The use of lifting strakes on boat hulls of the V-bottom type is essential to the stability of this type of craft in order to achieve higher operating speeds. Typical configurations for lifting strakes are shown in prior U.S. Pat. No. 3,117,544 to Schoell and in U.S. Pat. No. 4,027,613 to Wollard. As can be seen by reference to the transverse sectional views in these patents, the running surfaces in these V-bottom hull constructions all lie in the same plane of orientation normal to the keel of the boat. Accordingly, the lifting strake surfaces may be considered to be "add-ons" to the almost perfect V-shaped outline defined by the running surfaces. As alluded to above, the lifting strakes are typically formed of two generally perpendicular surfaces which define an included angle of almost 90 degrees between the adjacent pairs of running surfaces.
The relative positioning of the running surfaces which define the general outline of the vee, and the configuration of the lifting strakes in conventional V-type hull bottom designs, gives rise to several serious shortcomings. For example, the relative positioning of the running surfaces and the overall configuration of the strakes means that a plurality of longitudinal protrusions will be defined along the bottom surface of the hull and with portions thereof which will lie essentially perpendicular to the surface of the water to provide the needed lift. Accordingly, as the general orientation of the hull to the water's surface is altered by a high speed turn, for example, hydrodynamic forces will be exerted on the outside surface of the bottom against the strake which will in turn act like a rudder. These forces will tend to force the chine or spray wall disposed on the outside of the turn downwardly against the surface. This presents an extremely dangerous situation during high speed turns particularly for novice boaters as described, for example, in U.S. Pat. No. 4,726,310 to Ard, et al. Experienced boaters are customarily forced to throttle down prior to executing virtually any turn because of these forces.
A related problem presented by the use of conventional strakes resides in the relative performance characteristics of the engine itself. Specifically, conventional strake designs tend to generate air bubbles which can become entrained against the propeller and cause prop ventilation. Prop ventilation robs the powerboat of needed horsepower and requires the operator to throttle down until the entrained air dissipates or is otherwise displaced from the surface of the blades. This is obviously frustrating especially for experienced operators who, despite their skill, routinely experience prop ventilation while executing turns and especially in virtually all high speed turns.
One material offshoot of the prop ventilation problem resides in the relative positioning of the cavitation plate and of the prop on stern drive powerboats. Specifically, and in order to minimize incidents of prop ventilation, the cavitation plate and prop must be positioned at a relatively lower elevation to the keel than is desired for optimum efficiency based on any given horsepower. Stated otherwise, the lower positioning of the propeller increases the effective drag on the boat. The significant advantages which can flow from the ability to position the prop even a single inch closer to the keel are recognized in the prior art as discussed, for example, in the background of U.S. Pat. No. 4,619,215 to Wood, et al. As described there, the relative drag caused by the prop and housing increases exponentially with increasing propulsion unit submergence. Thus, it is desired to position the cavitation plate and propeller as close to the transom as possible when, for example, the lower unit of a stern drive motor is fully trimmed.
Although the prior art has recognized the significant drawbacks associated with conventional boat hull designs, no satisfactory solution to the related problems of stability in turns and performance have yet been devised. For example, the design shown in Wood, et al. U.S. Pat. No. 4,619,215 incorporates a series of adjacent steps wherein the planing surfaces of the strakes disposed between adjacent running surfaces include the problematic generally perpendicular surfaces and with the corresponding drawbacks described hereinabove. And, in recent U.S. Pat. No. 4,903,626 to Haines, it is proposed to incorporate a transverse recess and step in the hull bottom in order to permit the propeller of the outboard engine used there to be elevated, but at the obvious expense of stability. Furthermore, while the structure of Haines does appear to incorporate an improved strake configuration in comparison to the prior art, the interior strake surfaces shown there are intentionally bifurcated well short of the stern which will in fact lead to the generation of additional turbulence and corresponding reductions in performance resulting from increased incidents of prop ventilation.